The study evaluated a total of 21 patients with cancer pain including those with additional respiratory problems. We analyzed random plasma samples from patients using our GC-NP procedure and kept a validation of the RIA assay used for this study. We analyzed a total of four patient sets of plasma samples using our GC method. We have recently analyzed data from 10 steady-state post-infusion studies in 7 patients to estimate the disposition of fentanyl in cancer patients. Fentanyl, with its redistribution controlling its duration of action, appears to have a significantly (p less than 0.05) prolonged half-life in cancer patients (range: 6-29 hrs.) compared to normal volunteers (mean: 5 hrs). This diminished clearance may reflect a higher tissue uptake or a more appropriate study design for obtaining disposition parameters of fentanyl.